Single pyrotechnic hybrid inflator

ABSTRACT

An inflator for an air cushion including a pressure vessel comprising a hollow sleeve for storing a quantity of inert gas such as Argon. One end of the sleeve is closed by a first pyrotechnic actuator assembly while the other end of the sleeve may include a closed end or another pyrotechnic actuator assembly. The pressure vessel is secured within a diffuser which directs inflation gases into the air cushion. The pressure vessel in cooperation with the diffuser defines various regions which assist in reducing the gas turbulence and heat transfer between the gas and the diffuser.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a device for inflating an air cushion,air bag, or the like.

Inflatable bag restraint systems have been shown to reduce theseriousness of injuries and number of fatalities resulting in motorvehicle accidents. There exists a number of means for inflating an aircushion or air bag such as utilizing a quantity of stored gas which isselectively released to expand the air bag. Alternatively, a gas sourcederived from a gas generating material propellant such as sodium azide,which upon ignition thereof generates a sufficient quantity of gas toexpand the air bag. The third type of gas source results from acombination of the stored compressed gas and a gas generating orenhancing material. This last device is often referred to as anaugmented gas or hybrid inflator. Various hybrid inflators have beenshown in the past such as those illustrated in U.S. Pat. Nos. 3,756,621and 3,895,821. The inflator shown in U.S. Pat. No. 3,756,621 uses aseparate squib or initiator to ignite the propellant and an actuator toopen an exit passage to initiate compressed gas flow. U.S. Pat. No.3,895,821 mounted a single squib outside the pressurized environment ofthe pressure vessel to ignite the propellant. In that invention a singlesquib and propellant chamber or housing is placed in a compressed inertgas environment. Upon initiation of the propellant, a heated media isgenerated, comprising hot gas and particulates which are directed by adischarge nozzle into a small mixing cavity or chamber adjacent arupturable disk causing same to burst, initiating gas flow into an airbag. Hot gases continue to be emitted from the propellant chamber andmix with the cold pressurized gas in a small mixing chamber beforecontinuing into the bag to inflate same. The present invention yieldsadvantages in relation to the prior art in that the number of leakpassages are reduced, electrical leads are shielded from the harshenvironment of the inflation gases, and the inflation rate iscontrolled.

It is an object of the present invention to provide a hybrid inflatorwhich can rapidly and efficiently generate a sufficient quantity of gasto inflate a cushion or air bag during a vehicle crash situation. Afurther object of the present invention is to provide an inflator for anair cushion or air bag which improves upon the deficiencies of the priorart.

Accordingly the invention comprises: a hybrid inflator for an cushioncomprising in one embodiment a hollow, cylindrical sleeve enclosed atboth ends by pyrotechnic actuator assemblies. The enclosed sleevecomprises a pressure vessel for the storage of a quantity of pressurizedinert gas such as Argon. A trace amount of helium may be present tofacilitate leak testing of the pressure vessel. The first actuatorassembly comprises an actuator, detonator or squib for generating ashock wave to break a frangible disk member to enable gas flow throughflow orifices associated with the first actuator assembly. A secondactuator assembly is positioned opposite from the first actuatorassembly and includes another detonator, initiator, squib or the likefor initiating the burning of a quantity of propellant. The propellantelevates the temperature of the stored inert gas to increase its volumeprior to inflating the air cushion. In one embodiment of the invention asecond frangible disk, forming part of the pressure vessel, ispositioned opposite the propellant and upon being broken permits heatgenerated by the propellant to enter the pressure vessel. In anotherembodiment of the invention, upon breaking the second disk a second flowpath is created to permit the egress of the heated inflation gas outfrom the pressure vessel. In an embodiment of the invention, only asingle actuator assembly is used which upon the breakage of thefrangible disk permits the stored gas to flow out of the pressure vesselin a direction generally about the propellant. The inventionadditionally includes a diffuser which supports the inflator andprovides a flow passage to the air cushion. The diffuser also supportsthe air cushion. The diffuser envelopes the inflator in a manner tocreate relatively large volume regions downstream of any gas outlet inthe pressure vessel. This design reduces gas turbulence and reduces theamount of heat transfer between the heated inflation gas and thediffuser.

Many other objects and purposes of the invention will be clear from thefollowing detailed description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 illustrates a front cross-sectional view of the presentinvention.

FIG. 2 illustrates a side end view of the present invention.

FIG. 3 illustrates an alternate embodiment of the generator housingassembly.

FIG. 4 shows a cross-sectional view of the propellant used.

FIG. 5 is an enlarged view of an exemplary weld joint.

FIG. 6 is a partial, projected view of a diffuser.

FIG. 7 illustrates prior art diffuser.

FIG. 8 is a side view of the diffuser with a folded air bag.

FIG. 9 is a diagramatical view of an air bag.

FIG. 10 illustrates an alternate construction of a portion of thepresent invention.

FIG. 11 illustrates a graph of inflation curves.

FIG. 12 illustrates an alternate embodiment of the present invention.

FIG. 13 illustrates a further embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to FIG. 1, there is shown a hybrid inflator 10 forinflating an air cushion such as an air bag usable within a vehicleoccupant restraint safety system. The inflator 10 comprises a pressuretank generally shown as 20 which includes a hollow sleeve 22. Thepressure tank 20 in the space 24 is filled and pressurized with an inertgas such as Argon. The gas may also be a mixture of Argon and anotherinert gas such as helium. It is contemplated that the amount of heliumbe approximately 2% by volume of the Argon gas. The purpose of using thesecond inert gas is to provide a means for detecting defects in thevarious weld joints of the hybrid inflator which would cause leakage.Devices for sensing the presence of helium such as mass spectrometersare well known in the art. The pressure vessel, and more particularlythe sleeve 22, is enclosed at its respective ends 26 and 28 by aninitiator housing assembly 30 and by a generator housing assembly 80,which may be viewed as part of the pressure vessel 20.

The initiator housing assembly 30 includes an initiator housing 32comprising a necked down, narrowed portion 34 and a wider end portion36. Threadably inserted within the narrowed portion 34 is a spacer anhousing 38 having a central opening 39 to receive a detonator 40 ofknown construction. Extending from the detonator are actuation leads orwires 42. An O-ring 44, provides a seal between the detonator 40 and thespacer 38.

Attached to the initiator housing 32, forming part of the assembly 30,is a manifold assembly 50. The manifold assembly comprises an outercylindrical portion 52, attached such as by welding (see numeral 54), tothe initiator housing 32. The manifold assembly 50 further includes asmaller diameter cylindrical portion 56 recessed relative to the outerportion 52, which is adapted to mate with and receive one end 26 of thesleeve 22. The sleeve 22 and manifold assembly 50 are attached such asat the circumferential weld 58. The manifold assembly further includes alarge, flat edge orifice 60 enclosed by a frangible member such as aburst disk 62. A suitable burst disk 62 may be fabricated of nickel orstainless steel. The burst disk is attached to the manifold assembly 50at a circumferential plasma weld 63 facing the pressurized gas.

Press fit against the wall of the smaller diameter portion 56 is anapertured screen 64 comprising a plurality of openings 66, positionedabout a central opening 68, coaxial with the center of the detonator 40.Upon assembly, the screen 64 is slightly deformed inwardly by the narrowportion 34 of the initiator housing 32 to prevent rattling. The screen64 prevents large objects such as portions of the disk 62 from enteringthe air bag. The outer cylindrical portion 52 of the manifold assembly50 includes at least two orifices 70a and b, diametrically opposed, toprovide for a neutral thrust, wherein the total flow area of theorifices 70a and 70b is significantly smaller than the area of theopening 60. Upon actuation of the detonator 40 a pressure, or shock waveis created to break the frangible member or disk 62 permitting at leaststored inflation gas to exit the pressure vessel 20. This initialinflation is sometimes referred to as a cold inflation.

In the present invention the narrow orifices 70a and b regulate the flowrate of the inflation gas exiting the pressure vessel 20. The orifice 60about which the burst disk 62 is positioned does not generate anysubstantial pressure drop due to its large size. This constructionyields the advantage of standardization of design of the inflator fromone sized model to another. The burst disk 62 to orifice 70a and 70bdiameter relationship establishes the rupture point of the burst disk 62as a safety relief device or valve in the event of an overpressurization of the pressure vessel resulting from overheating orflattening of the pressure vessel due to misuse.

The gas generator housing assembly 80 comprises a stepped housing 82having an enlarged end 84 mating with the other end 28 of the sleeve 22of the pressure tank 20. The sleeve 22 and housing 82 are joined at acircumferential weld 87. The housing 82, at its inner end 86, includes acentral opening 88, covered by a thin burst disk 90 typically fabricatedof stainless steel. The disk 90 is welded to the housing 82 in a manneras discussed above.

FIG. 3 illustrates an alternate embodiment of the generator housingassembly 80 in which the end 86, at the previous location of the opening88, includes a plurality of smaller openings 92, covered by the burstdisk 90. In this embodiment the housing 82 material, between theopenings 92, provides additional support for the burst disk 90,permitting same to be made significantly thinner than the burst disk 90shown in FIG. 1. A typical thickness of the burst disk 90 in thissituation would be 0.1 mm (stainless steel). Returning to FIG. 1,positioned within the hollow interior of the housing 82 is a grain trap94 having a plurality of openings 96 therein, which prevent extrusion ofthe burning propellant 100 into the openings 96. Upstream of the graintrap is a quantity of extruded or shaped propellant 100. The propellant100 may be Arcite such as that disclosed in U.S. Pat. No. 3,723,205,which is incorporated herein by reference.

The propellant 100 is biased against the grain trap 94 by a wave washer102. The thickness of this resilient member, i.e., wave washer 102, maybe varied to accommodate varying lengths of propellant 100. Threadablyreceived within the housing 82 is a housing 104 of having a centralopening 106 which terminates at one end thereof in a conical, divergentnozzle 108. Received within the oPening 106 is another detonator orinitiator 110 of known design, having a plurality of electrical leads112 attached thereto. Within the divergent nozzle 108 is an ignitionenhancing material 109 comprising boron potassium nitrate whose flametemperature and quantity are suitable for instantaneously igniting thepropellant 100.

With reference to FIG. 4, this figure illustrates a cross-sectional viewof the propellant 100. The exterior 120 of the propellant 100 is formedin a cloverleaf-type pattern with each cloverleaf having a centralopening 122. The purpose of this construction is to provide for arelatively constant propellant burn rate. As the propellant 100 burnsits exposed area remains generally constant, that is, as the exterior ofthe propellant burns its outer surface area reduces while the surfacearea about each of the cylindrical openings 122 increases, yielding auniform burn surface and a resulting controllable burn rate. The burnrate is further controlled by the flow area of the central openings 92or 88. As can be seen, the pressure in the generator housing 82 (whichcontains the propellant 100) as determined by the openings 92 or 88 isalso effective in controlling the total propellant burn time.

The inflator 10 further includes a diffuser 130 comprising end caps 132and 134, and a main portion 140. The shape of each end cap can be seenin FIG. 2. The end caps 132 and 134 are secured respectively to theinitiator housing 32 and gas generator housing 80. This securement maybe accomplished by providing the gas generator housing 82 with aplurality of extensions or serrations 150, which extend through openings152 in the end cap such as 134. These extensions 150 during assembly arecrimped over, holding the end cap 134, diffuser 130 and pressure vessel20 in place. The other end cap 132 may be secured to the initiatorhousing 32 through a like plurality of extensions or serrations 156received through openings 158 in the end cap.

The gas generator housing assembly 80, or alternatively, the initiatorhousing assembly 30, may further include provision for a fill tube 160of normal construction through which the inert gases are communicated tothe interior 24 of the pressure vessel 20. Upon filling the pressurevessel with gas, the fill tube 160 is crimped at a location such as 162and sealed at location 163. Subsequent to the seal weld operation thecrimped portion 162 of the tube 160 may be mechanically squeezed toreopen same to provide for direct communication of inflation or test gasto the welded or sealed joint (at location 163).

Reference is made to FIG. 5 which illustrates an exemplary weld jointsuch as 58. The following is also applicable to the other weld jointsused within the inflator 10 such as 54 and 87. More specifically, FIG. 5illustrates the junction of the left hand end 26 of the sleeve 22 to themanifold assembly 50. During fabrication of the various assemblies 30and 80, and after complete fabrication and filling the inflator 10 withgas, each of the weld joints 58 and 87, are leak tested. To facilitatesuch testing as well as to insure the efficacy of each of these weldjoints the present invention contemplates that the various pieces ofmetal to be welded will be sized and fit together, prior to suchwelding, so that they touch only in the vicinity of the weld generallyavoiding the use of long interference, threaded or press fit contactareas. As such, FIG. 5 shows that the portion 56 of the manifold 50 isslightly spaced (see numeral 166) from the sleeve 22. In this manner,the stored pressurized gas or alternatively a test gas, is permitted tomigrate in a relatively unobstructed manner to the point of the weldsuch as 58. By constructing the fit of the various components in thismanner, a leak arising from a defect in the weld can be readily detectedduring testing of the pressure vessel. This construction is in contrastto the prior art which teaches the use of threadable interconnections oralternatively, interference and press fit connections. Use of a threadedor press fit connection impedes the migration of stored or test gas tothe weld point, and as such, leak tests done on prior art inflators didnot always detect a defect in the weld because migration of gas to theweld point was significantly restricted, i.e., gas could not migrate tothe weld point by the time the pressure vessel was tested. Thisdeficiency in the prior art resulted in what is called infant mortalitytypes of failures. Should threaded connections be required or desired, amilled slot 254 (see FIG. 9) extending the length of the threads wouldprovide an unrestricted passage of the gas to the joint under test. FIG.9 presents an alternative attachment of parts of the present inventionshowing a screw thread connection. There is shown a generator housing 82having threads 250 received within threads 252 in the end 28 of thesleeve 22. A milled slot 254 is provided in one of the sets of threadsto permit the direct migration of gas to the weld joint 87. It should beappreciated that the slot 254 can be in either the housing 82 or thesleeve 22 of the pressure vessel 20.

FIGS. 2 and 6 illustrate various views of the diffuser 130. FIG. 6,shows a projected partial view of some of the major components formingthe diffuser. The diffuser 130 is essentially a can of specific shapedesigned to cradle and support the pressure vessel 20. As will be seen,the diffuser 130 also supports an air bag. The diffuser 130 incooperation with the pressure vessel, also provides a conduit tocommunicate the inflation gas to the air bag. The diffuser 130 shown inFIG. 6 includes the main portion 140 and end caps 132 and 134 shown inFIG. 1. The main portion 140 may be fabricated of a lower assembly 180and an upper assembly 182. The upper and lower assemblies 182 and 180,respectively, provide for a three location axial interference fit withthe pressure vessel 20. In cross-section the shape of the diffuser 130is somewhat triangular to provide a three-point contact with thepressure vessel 20. Toward the rear or lower portion as seen in FIG. 6of the diffuser its shape generally follows that of the cylindricalpressure vessel. Toward the front of the diffuser, i.e., in thedirection of the inflating air bag, it departs from the pressure vesselto define volumes 183a and b. The lower assembly comprises an openstructure having at its lower extreme a longitudinally extending trough184. The lower assembly further includes a plurality of tabs 186designed to fit through a like plurality of openings 188 formed in theupper assembly. The tabs 186 may be bent, crimped or otherwise securedin place. In cross-section the walls 190a and b taper inwardly tointersect with the circular pressure vessel 20 at least along a linecontact 192a and b. The walls 190a and b may be arcuately shaped, asshown more clearly in FIG. 6, to provide an interference fit with agreater area of the pressure vessel 20. Positioned within the trough 184and extending therefrom are a plurality of mounting lugs 204, which maybe useful in mounting the inflator 10 and air bag 202 to cooperatingportions of the vehicle's structure, avoiding the need for an additionalhousing (see FIG. 7) to hold the diffuser and inflator, as had been usedin the prior art. Various techniques for attaching the lugs 204 to thelower assembly 180 of the diffuser 130 are known in the art.

The upper assembly 182 can be formed with a central longitudinallyextending trough 194 which provides at least a point contact (or contactarea) at 196 along the pressure vessel 20. The trough 194 may bearcuately shaped as shown in FIGS. 2 to contact a larger area of thepressure vessel or flat as shown in FIG. 6. The axially extending troughprovides stiffness to the diffuser 130 permitting lightweight materialsto be used. The trough 194 is not essential to the invention and ifeliminated, the front 193 or top as seen in FIG. 6 of the diffuser wouldessentially be of planar construction. The upper assembly 182 mayfurther include a plurality of openings 200 to distribute inflation gasto an air bag 202 which is positioned thereabout. The orientation of theholes 200 may extend axially (shown in phantom line) along the top 193of the assembly 182 or radially or a combination thereof. The locationand position of the holes are chosen to assist in limiting anydeformation that may occur to the diffuser 130 upon generation of theinflating gases and to evenly distribute the generated gases to theinterior of the cushion or air bag.

An advantage of the increased (dead) volume, i.e., 183a, b and the useof the openings 200 in top 193 of the diffuser 130 is to decrease theturbulence in the inflation gas as it exits the pressure vessel andflows through the diffuser 130. Characteristic of prior artinflators/diffusers which typically were of circular cross-section (seeFIG. 7), was a high degree of turbulence in the inflation gas as itexited the pressure vessel. This turbulence assisted in creating a largeheat transfer between the heated inflation gas and the prior artdiffuser. Heat lost from the inflation gas reduces its volume and hencethe efficiency at which the air bag is inflated. Use of a greater amountof stored gas and/or propellant was required to compensate for thiseffect in the prior art. In contrast, the present invention reducesturbulent flow, reduces the pressure drop across the diffuser, andreduces the amount of heat transfer to yield more efficient performance.FIG. 7 which is illustrative of the prior art, shows a typicalcylindrically shaped inflator 10' positioned within a cylindrical,closely spaced diffuser 130'. The inflator may be of the hybrid typesuch as the present invention or alternatively, a sodium azide basedinflator as is known in the art. Inflation gas exited openings such as220 flows turbulently through the diffuser 130' to inflate an air bag202 which is diagramatically illustrated. The diffuser 130', inflator10' and air bag are typically secured within a reaction can 222, whichis then secured to a portion of the vehicle such as its instrumentpanel. Reference is made to numeral 224, which illustrates a trappedvolume 226 within the reaction can 222. This volume was not effectivelyutilized since the air bag 202 could not be tightly folded therein.

With regard to the present invention, FIG. 8 diagramatically illustratesan air bag 202 secured about the inflator 10. More particularly, the airbag 202 comprises an open end 210 into which is received the diffuser130 (see FIG. 10). The air bag 202 proximate its end 210 may include aplurality of extending flaps 212a and b, which are received about thediffuser 130 in an overlapping manner (see FIG. 8) with the mountinglugs 204 extending therethrough. The air bag 202 may be maintained inits folded configuration by enveloping same with a thin tearable cover214 shown in dotted line in FIG. 8. This feature allows the unit to bedirectly attached to the vehicle mounting structure without the need foran intermediate housing or reaction can. In this case the vehicleinstrument panel could include a cavity or shape similar to the reactioncan shown in FIG. 7. In contrast, the non-circular cross-section of thepresent diffuser 130 relative to the generally cylindrically shapedinflator 10 or pressure vessel 20 is arranged to minimize the surfacearea to which the inflation gases are exposed and also to minimize thepressure drop to reduce heat loss without affecting the overall packagesize of the unit. From FIGS. 1 and 6 it should be appreciated that theexit orifices 70a and b direct inflation gases directly into the volumes183a and b of the diffuser 130. In addition, a further advantage of thepresent invention is achieved with regard to the aspect of folding theair bag and positioning it relative to the diffuser. By utilizing thegenerally flat top surface 193 of the diffuser provides an ideal surfaceupon which the air bag may be folded.

In view of the above, it is contemplated that the diffuser 130 may befabricated of lightweight material. More specifically, the lowerassembly 180 may be fabricated of aluminum, while the upper assembly 182may be fabricated of a high strength, low alloy steel.

Reference is made to FIG. 1 and more particularly to the orientation ofthe electrical wires or leads 42 and 112 extending from the actuator 40and initiator 110. As can be seen from FIG. 1, these leads or wires 42and 112, respectively, are exterior to the pressure vessel and as such,are not subject to the heat generated by the actuator 40 or initiator110 upon excitation. It is contemplated that the wires 42 will be fedfrom the right hand side of the inflator 10 as shown in FIG. 1, throughthe trough 184 and exit the inflator at its left side through an opening220 in the cover 134. This construction facilitates attachment to acontroller, eliminates loose and dangling wires and reduces the numberof electrical connectors needed. Correspondingly, the cleanliness of thegenerated gases in the present invention, are enhanced as the breakdownof foreign materials (such as due to the melting of the internal wires)is prevented for better management of effluent which also reducestoxicological concerns. In the prior art, such as illustrated by U.S.Pat. No. 3,756,621, the wires extended through the pressure vessel andwere subject to the extremely harsh environment generated uponactivation of propellant such as 100.

The following briefly describes a typical fabrication process that maybe utilized to assemble and test the inflator 10. The initiator housingassembly 30 is assembled by positioning the screen 64, if used, withinthe manifold assembly 50 and welding the manifold assembly to theinitiator housing 32 at location 54. The burst disk 62 is welded aboutthe opening 60 using a plasma weld process. At this time thissub-assembly does not include the actuator 40 and spacer 38. Theinterior of this assembly is evacuated in a test chamber to create avacuum, and a test gas such as helium is exposed to the pressure vesselside of the burst disk 62. A leak test is accomplished by testing forthe migration of helium across the burst disk weld. It is important tonote that helium test gas will be applied to the side of the burst diskwhich will tend to lift it from the surfaces it is welded upon. If testgas is applied oppositely, the test gas would tend to hold the burstdisk to these surfaces and mask a leak. Thereafter, the sleeve 22 isassembled to the manifold assembly 50 and welded at 58. The generatorhousing assembly 80 is similarly mounted to the sleeve and welded at 87.Actuation gas comprising Argon and a small percentage of helium, isplaced within the completed pressure vessel 20 and filled to itsoperating pressure which is approximately 3,000 psi. Thereafter, thewelds at locations 58 and 87 are leak tested. Subsequently, the spacer38 and actuator 40 are threadably received within the initiator housing32. The various components comprising the initiator housing assembly,i.e., the grain trap 94, propellant 100, spring disk 102, housing 104,and initiator 110 are assembled to the generator housing 82. Byfollowing this assembly technique, if the pressure vessel fails the leaktest, the various pyrotechnic related components need not be scrapped.Further, the present invention is well suited to a wide range is weldingtechniques since the pyrotechnic elements are not mounted duringwelding. In the prior art the welding technique was restricted to onewhich would generate a minimum heat affected zone so as not to ignitethe mounted pyrotechnic elements. Typically, an electron beam weld wasused, however, this technique is expensive and ill-suited for massproduction. Upon final assembly of the inflator 10, the air bag 202 issecured thereto.

The generator housing assembly is also tested for leaks at the interfacebetween the burst disk 90 and the generator housing 82 in a mannerdescribed above. The diffuser 130 comprising the end covers 132 and 134and the top and bottom assemblies 180 and 182 are thereafter attached toand about the inflator 10.

The dual pyrotechnic configuration of the present invention yieldsflexibility in that the rate of inflation of the air bag 202 can becontrolled. It is desirable to control the initial rate of inflation sothat the air bag does not too forcefully impact the occupant, especiallyan out-of-position occupant such as a standing child. In this regard,the inflator can be made operative by simultaneously initiating theactuator 40 and the initiator 110. This type of initiation yields themost aggressive air bag filling (see Curve A, FIG. 11). Alternatively,the actuator 40 may be initiated generating a shock wave which rupturesthe disk 62, causing an initial cold gas inflation as the stored Argoninflation gas exits the flow orifices 70a and b and begins to inflatethe air bag 202 (see Curve B, FIG. 11). Thereafter, for example, after atime delay 7, 10 or 16 milliseconds, the initiator 110 is activatedthereby causing the propellant 100 to burn, which in turn raises thetemperature of the remaining stored gas within the pressure vessel,thereby increasing the volume of gas available to inflate the air bag.In this manner, the initial cold gas inflation provides for an initiallyslower inflation rate of the air bag yielding a relatively soft contactwith the out-of-position occupant, which is thereafter followed by themore rapid inflation of the air bag upon activation of the initiator110. The sequence of activation of the actuator 30 and/or initiator 110depends to a large extent on the design of the vehicle and to the sizeof the passenger compartment. As an example, consider a frame or othersupport structure of a particular vehicle which tends to absorb less ofthe energy of a crash thereby transmitting more of same to the occupant.In this situation, the more aggressive inflation rate of Curve A may becalled for. If the vehicle is such that it absorbs more of the crashenergy, a less aggressive inflation rate such as Curve B would initiallyprovide for the gradual envelopment of the passenger. It can be seen,however, that based upon the graphs of FIG. 11, that maximum air baginflation is achieved at approximately the same point whether or not theinflation procedure is that for Curve A or Curve B.

In some situations it has been found that it is desirable to in factdelay activation of the initiator 110 for a period up to and perhapsexceeding 25 milliseconds. It can be appreciated that if the inflator 10of FIG. 1 is utilized, a significant amount of cold, stored inflationgas will have left the pressure vessel 20 during this extended timedelay period. FIG. 12 illustrates an alternate embodiment of the presentinvention which illustrates an inflator 300 suited to an inflationregime requiring extended time delay activation periods. FIG. 12illustrates the left hand portion of such inflator 300. It should beappreciated that the right hand portion is identical to that of FIG. 1.Inflator 300 comprises a generator housing assembly 80', including asecond manifold assembly 304 welded to a sleeve end 28' at acircumferential weld joint 305 to the sleeve 22'. The second manifoldassembly 304 is cylindrically shaped, terminating at a recessed end 306,having a sharp edge opening 308. The end 306 supports a second burstdisk 310. Positioned within the second manifold assembly 304 is thegenerator housing 82, comprising the propellant 100, initiator 110, etc.It should be appreciated that the burst disk 90, previously used toenclose the opening 88 of the housing 82, has been removed. An optionalscreen such as 312, similar to screen 64, may be positioned across theopening 308. The manifold assembly 304 further includes a second set ofgas flow orifices 320a and b, disposed in a generally thrust neutralcondition. Positioned about the sleeve 22' is the diffuser 130 discussedabove. In this embodiment of the invention the flow orifices 320a and320b are sized to be larger than the flow orifices 70, fabricated withinthe manifold 50. More particularly, the flow areas may have a ratio ofthree to one. As an example, the total flow area of the orifices 70a and70b may be approximately 0.32 square centimeters (0.05 square inches)wherein the total flow area of the orifices 320a and 320b may beapproximately 0.97 square centimeters (0.15 square inches). In responseto a signal indicative of a crash situation, the actuator 40 would beactivated thereby opening the burst disk 62 causing a cold inflation ofthe air bag as the stored inflation gases exit the orifices 70a and 70b,resulting in the reduced slope portion of Curve C, FIG. 11. Thereafter,the initiator 110 is activated causing the propellant 100 to burn awaythe second burst disk 310, thereby creating a second flow path for theremaining stored gas to exit the pressure vessel. Upon removal of theburst disk 310, the remaining stored gas exits the pressure vesselthrough the opening 308, the optional screen 312 and then exits throughthe larger orifices 320 and 320b, thereby increasing the rate at whichthe stored gases exit the pressure vessel which results in the increasedslope portion of Curve C. As the inflation gases exit the opening 308they pass directly across the heat generated by the propellant, therebyincreasing the volume of same as it exits the pressure vessel and flowsinto the air bag or cushion.

FIG. 13 illustrates a further alternate embodiment of the inventionhaving a single pyrotechnic element such as the initiator 104. Thestructure of this inflator 350 builds upon the alternate embodimentshown in FIG. 12. More specifically, the left hand portion of thisinflator 350 is identical to that of FIG. 12. The sleeve portion 302 ofthe pressure vessel terminates at its right hand side in an arcuately orperhaps spherically shaped surface 354. Attached to the end 352 is aretaining member such as the cup-like structure 356 welded thereto. Theends 358 of this structure 356 include the tabs such as 156 which, aspreviously mentioned, extend from the actuator housing 32 for attachmentto the diffuser end 132. A fill tube 360 is provided in the end 352 forfilling the pressure vessel with inert inflation gas. Upon activation ofthe initiator 110, the burst disk 310 is opened, thereby permittingheated inflation gas to exit the orifices 320a and b. The resultinginflation curve of this single pyrotechnic unit will essentially followthat of Curve A of FIG. 11.

Many changes and modifications in the above described embodiment of theinvention can, of course, be carried out without departing from thescope thereof. Accordingly, that scope is intended to be limited only bythe scope of the appended claims.

We claim:
 1. An inflator for an air cushion, comprising:a hollowcylindrical sleeve closed at one end thereof, including a fill means forreceiving inflation gas extending through the closed end and open at anopposite end; a generator housing assembly for enclosing the sleevecomprising a hollow manifold assembly, recessed into the sleeve andsecured at the opposite end thereof; the manifold assembly and sleevecomprising a pressure vessel to store the inflation gas at adeterminable pressure, the manifold assembly including a manifoldopening enclosed by a frangible member comprising a rupturable disk,forming part of the pressure vessel, the manifold assembly furtherincluding flow control means for controlling the flow of inflation gas,from the pressure vessel; the generator assembly includes a hollowgenerator housing extending into an open end of the manifold assembly,and includes a first housing end and a second housing end, the firsthousing end secured proximate the open end of the manifold assembly, thesecond housing end includes at least one opening positioned apart andgenerally in line with the manifold opening wherein generator housingassembly further includes a grain trap including a plurality of trapopenings positioned proximate the second housing end, a quantity offormed propellant and a resilient member for biasing the propellant intothe grain trap and a pyrotechnic actuator means spaced from theresilient member for initiating, upon activation, the burning of thepropellant.
 2. The inflator as defined in claim 1 wherein the closed endof the sleeve is concave inward and wherein the inflator furtherincludes securing means, conformal in shape with the closed end forsecuring the sleeve to a cooperating diffuser.
 3. The inflator asdefined in claim 1 wherein the actuator means includes a divergentnozzle spaced from and facing the propellant.
 4. The inflator as definedin claim 3 wherein the actuator means includes an ignition enhancingmeans for rapidly initiating burning of the propellant in the divergentnozzle.
 5. The inflator as defined in claim 4 wherein the ignitionenhancing means includes a quantity of boron potassium nitrate.
 6. Theinflator as defined in claim 1 wherein the actuator means is removablyreceived within the generator housing.
 7. The inflator as defined inclaim 6 wherein the actuator means is located exterior to the storedgas.
 8. The inflator as defined in claim 1 wherein the first housing endincludes attachment means for attaching the pressure vessel to thediffuser.
 9. The inflator as defined in claim 8 wherein the diffuser isin communication with the flow control means, and supports the pressurevessel and directs inflation gas into an air cushion, the diffuserincluding a lower portion adapted to support a lower portion of thepressure vessel, the diffuser further includes an upper portion adaptedto mate along with an upper portion of the pressure vessel, the upperportion including a plurality of openings to permit inflation gas toflow thereacross, and defining in cooperation with the pressure vesseltwo volume regions proximate the upper portion of the pressure vessel soas to provide a means for reducing turbulence of the inflation gas andto reduce the heat transfer of the inflation gas with the diffuser. 10.The inflator as defined in claim 9 wherein the diffuser includes endcaps, for enclosing respective ends of a main portion of the diffuser.11. The inflator as defined in claim 10 wherein the diffuser comprisesattachment means such as a plurality of bolts extending therefrom forcontaining the air bag and for providing means for directly attachingthe diffuser to vehicle support structure.
 12. The inflator as definedin claim 1 wherein a screen is positioned about at least one opening inthe generator housing end and mated with a portion of the manifoldassembly.
 13. An inflator for an air cushion, comprising:a hollowcylindrical sleeve closed at one end thereof, including a fill means forreceiving inflation gas extending through the closed end and open at anopposite end; a generator housing assembly for enclosing the sleevecomprising a hollow manifold assembly, recessed into the sleeve andsecured at the opposite end thereof; the manifold assembly and sleevecomprising a pressure vessel to store the inflation gas at adeterminable pressure, the manifold assembly including a manifoldopening enclosed by a frangible member comprising a rupturable disk,forming part of the pressure vessel, the manifold assembly furtherincluding flow control means for controlling the flow of inflation gas,from the pressure vessel; the generator assembly includes a hollowgenerator housing extending into an open end of the manifold assembly,and includes a first housing end and a second housing end, the firsthousing end secured proximate the open end of the manifold assembly, thesecond housing end includes at least one opening positioned apart andgenerally in line with the manifold opening, wherein the manifoldassembly is welded to the sleeve in a manner to permit the unobstructedmigration of stored gas to the point of weld.
 14. An inflator for an aircushion, comprising:a hollow cylindrical sleeve closed at one endthereof, including a fill means for receiving inflation gas extendingthrough the closed end and open at an opposite end; a generator housingassembly for enclosing the sleeve comprising a hollow manifold assembly,recessed into the sleeve and secured at the opposite end thereof; themanifold assembly and sleeve comprising a pressure vessel to store theinflation gas at a determinable pressure, the manifold assemblyincluding a manifold opening enclosed by a frangible member comprising arupturable disk, forming part of the pressure vessel, the manifoldassembly further including flow control means for controlling the flowof inflation gas, from the pressure vessel; the generator assemblyincludes a hollow, generator housing extending into and secured to themanifold assembly, a quantity of propellant resident in the generatorhousing and a pyrotechnic actuator means for initiating, uponactivation, the burning of the propellant, wherein the manifold assemblyis welded to the sleeve in a manner to permit the unobstructed migrationof stored gas to the point of weld.